JPS5846879B2 - semiconductor laser equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser device used as a light source of an information processing device.

2. Description of the Related Art Conventionally, for example, as an information processing apparatus, there is a device (Japanese Patent Laid-Open No. 47-37407) that reproduces video information by irradiating light onto a carrier that stores video information concentrically or spirally.

In such a device, it is conceivable to use a semiconductor laser as a light source to reduce the size of the device.

However, semiconductor lasers have a drawback in that their output fluctuates widely due to changes in temperature, etc., and their stability is low.

That is, injection type semiconductor lasers, especially at room temperature or near room temperature, have a continuous or nearly continuous duty ratio (Duty R).
In a semiconductor laser that operates in an atio), the oscillation threshold current increases as the temperature of the device increases.

For example, I Hayashi and several other authors have published an article in the American academic journal ``Journal of Applied Physics''.
plied physics ) J Vol. 42 No. 1929
Paper submitted to page (1971) rGaAs-A4
As reported in ``Gat-XAs Double Heterojunction Injected Laser'', when a semiconductor laser is driven with a constant current, the laser output changes as the ambient temperature changes.

That is,... threshold current = Jth 17) Temperature 1f-
f, Jth: JoeXp (T/T) (1) (
However, both J and T are parameters that determine the change in "passive current" with respect to temperature, and are determined depending on the element.

). Double heterojunction structure GaAs-A-
Consider the case where a GaAs laser is operated.

When the temperature T of the semiconductor laser element changes by AT, the threshold current ''Jth becomes as follows from equation (1).

If the operating current of the semiconductor laser device is J, then the change in laser output P due to the temperature change of the device (P is as follows).

(where ε is a parameter that determines the operating point of the semiconductor laser element.

).

Therefore, if the temperature of the element rises by 6℃ from the operating point,
Laser power is halved.

Of course, if the device is used with a large ε, the rate of change in laser output with respect to temperature changes will decrease, but on the other hand, the rate of deterioration of the semiconductor laser device will increase as the operating current increases, so use the device as close to the threshold current as possible. It is desirable to operate with

As mentioned above, the optical output of a semiconductor laser is easily affected by the temperature of the element, so under normal conditions where no means are taken to maintain a constant temperature, other methods are required to maintain the laser output at a steady state. A means is required.

If such means for standardizing laser light output were to disappear, it would be difficult to use semiconductor lasers as light sources for information processing equipment, and gas lasers with stable optical output would have to be used. Light weight cannot be achieved at all.

Conventionally, semiconductor laser devices equipped with such means have not been commercially available, but in the field of gas lasers, a portion of the laser light is split into a beam 0 splitter (
The extracted laser light is extracted using an optical system such as a 5plitter), and the extracted laser light is detected by an appropriate photodetector. If the laser output changes, the detected output is returned to the gas laser excitation power source and sent to the gas laser. Means is employed to maintain the laser output constant by controlling the supply input of the laser.

In the case of a semiconductor laser, the same method can be adopted, but introducing an optical system such as a beam 0 splitter into a semiconductor laser device, which is designed to be small and lightweight, will increase the size of the device.

In view of this, the present invention uses a semiconductor laser device as a light source of an information processing device, and attempts to make the output light constant by eliminating changes in the yj5 laser output due to temperature changes of the semiconductor laser element. be.

In order to achieve this object, the present invention uses the light in one direction of a semiconductor laser element that emits light in both directions as light for information processing, installs a light receiver that receives light in the other direction, and furthermore installs a light receiver that receives light in the other direction. The present invention is characterized in that it includes means for detecting a variation in the amount of emitted light received by the laser beam, and means for controlling the optical output of the semiconductor laser element so as to compensate for the variation in the amount of received light.

The present invention will be explained below with reference to Examples.

FIG. 1 is a diagram schematically showing the configuration of an embodiment of a semiconductor laser device according to the present invention.

This semiconductor laser device includes a semiconductor laser element 1, a copper heat sink 8, an electrothermal cooling element 12, a radiation fin 13, and a photodetector 5, 6 is an amplifier for the output of the photodetector, and 7 is a variable constant voltage generator and a control. It is a power source for a thermoelectric cooling element including a circuit.

The semiconductor laser device 1 is a GaAs-A double heterostructure laser, and when a current higher than the threshold current is passed through the power supply 14 and the load resistor 15, laser oscillation occurs, and the two at both ends of the active layer 2 Laser beams 3 and 4 are emitted from the cleavage planes (ie, the reflective surfaces), respectively.

The laser beam 3 can be used as a light source for optical communications, optical information processing, spectrometers, etc., and the laser beam 4 emitted from another reflective surface is received by a photodetector 5 placed close to the semiconductor laser element 1. The surface is irradiated.

As the photodetector 5, for example, in a GaAs-based semiconductor laser (with an oscillation wavelength in the range of about 7500 to 900A), a solar cell made of Si, a PIN photodetector, etc. are convenient in terms of sensitivity characteristics.

In this embodiment, the photodetector 5 is used in a short-circuit current mode that is relatively stable with respect to temperature.

The photodetector 5 is electrically insulated from the heat sink 8 by a thin insulating layer 9.

The temperature Tj of the active layer 2 of the semiconductor laser device 1 is determined by the electrical input supplied to the laser device 1, the ambient temperature Ta, and the current flowing through the thermoelectric cooling element 12.

The voltage and current supplied to the laser element are V and ■, respectively.
, where the temperature of the heat sink 8 is Th.

Here, θ is the thermal resistance of the laser element 1 and the heat sink 8, and I th is the threshold current of the laser element 1.

The optical power P of the laser is given by:

Here η is a proportionality constant. From the three equations above, the laser output can be determined as a function of current and heat sink temperature.

FIG. 2 is a characteristic diagram schematically showing the calculation results, where the vertical axis represents the laser output P, the horizontal axis represents the current ■, and the parameters are the heat sink temperature Th, where Th3>Th1>Th2.

From FIG. 2, it can be seen that there are various combinations of current and heat sink temperature necessary to obtain the laser output P1.

When the heat sink temperature is fixed, there are two types of current values required to obtain the laser output P1, but of course,
Lower current values are preferable.

When the heat sink is equipped with the thermoelectric cooling element 12 as in the embodiment shown in FIG. 1, the temperature of the heat sink can be selected within a considerable range.

Now, if the heat sink temperature is Th1, the required current is .

From the viewpoint of obtaining the necessary laser output with as little current as possible, it is desirable to select the heat sink temperature Tht lower than the ambient temperature Ta.

Here, AT is the temperature difference maintained by the thermoelectric cooling element 12 and is determined by the current supplied to the thermoelectric element.

Now, the ambient temperature Ta changes by δT due to some unknown reason,
Assuming that the heat sink temperature becomes Th3 (=Th1+θT) and the current supplied to the thermoelectric cooling element does not change, the laser output decreases from the predetermined laser output value P1 to P3.

In the embodiment of FIG. 1, the signal proportional to the laser output 4 monitored by the photodetector 5 is amplified by the amplifier 6 and then converted to a reference value (i.e., a predetermined laser output value P1 in this embodiment). The current supplied from the power source 1 to the thermoelectric cooling element 12 is changed so that the variation from the reference value approaches zero.

In the above case, the temperature difference (T) maintained by the thermoelectric cooling element is changed to (T
It will be changed to 10aT.

Temperature control using a thermoelectric cooling element has a fast response (less than 1 second)
Also, it has the advantage that the current can be made higher or lower than the ambient temperature depending on the polarity of the current, so it has the advantage that the laser output can be kept constant even in an environment where the ambient temperature fluctuates significantly.

For example, output fluctuations can be suppressed to within 5 degrees when the ambient temperature is in the range of 110 degrees Celsius to 45 degrees Celsius.

Furthermore, another advantage of this embodiment is that the monitoring laser beam 4 is used independently of the laser beam 3 to be used.

That is, since the laser beams 3 and 4 are emitted from the same optical cavity, their outputs are proportional to each other, so by controlling the laser output 4 to be constant, the amount of laser beam 3 to be used can be reduced. Output can be kept constant.

This is convenient when an optical fiber or the like is brought close to the laser element 1 and the laser beam 3 is directly introduced into the fiber, since a monitoring optical system is not required.

If the reflectance of the two reflective surfaces is equal, the magnitudes of laser outputs 3 and 4 are equal, but output 4 for monitoring may be small, so the reflective surface from which output 4 is taken out is coated with an insulating film and metal. It is preferable to coat the film to increase the reflectance.

This is because by increasing the reflectance of one reflective surface,
This is because the threshold current value for oscillation can be reduced.

Furthermore, in this embodiment, since the photodetector 5 is installed on the same heat sink 8 as the semiconductor laser element 1, the temperature of the photodetector 5 is also kept almost constant, and therefore the sensitivity of the photodetector is It also has the advantage of being less affected by ambient temperature.

Note that if the output of the semiconductor laser element is directly modulated, it is necessary to incorporate a low-pass filter into the amplifier 6.

At this time, the time average value of the laser output is kept constant.

Furthermore, the embodiment shown in FIG. 1 has the advantage that the photodetector is also kept at a substantially constant temperature, so that the sensitivity of the photodetector is also kept substantially constant.

FIG. 3 shows a schematic configuration diagram of another embodiment of the semiconductor laser device according to the present invention.

In FIG. 3, of the two reflected laser beams emitted from the semiconductor laser device 1, four 1/- laser beams are irradiated onto a photodetector 5 mounted on a heat sink.

The output obtained by the photodetector 5 is amplified by an amplifier 6 and compared with a value corresponding to a predetermined laser output P1, and the input power supply 14' to the laser element is adjusted so as to cancel out the corresponding fluctuation.
control.

In this embodiment, unlike the configuration of the embodiment shown in FIG. 1, the temperature of the heat sink is not controlled and changes depending on the ambient temperature, so the ambient temperature of the laser element 1 changes and the laser output also changes. It adjusts the power supplied to the element to cancel out changes in laser output.

As can be seen from the characteristic diagram in Figure 2, the continuous operation L.
In an operating state with a nearly continuous duty ratio, the maximum value of the laser output that can be obtained is determined by the ambient temperature, so this embodiment is difficult to use under conditions where the ambient temperature fluctuates greatly.

Furthermore, as is clear from Figure 2, there are operating conditions in which the optical output decreases as the current increases, but it is undesirable to control the output under such conditions, and it is not desirable to control the output under such conditions. It should work under the conditions.

Therefore, this embodiment can precisely control the optical output when the ambient temperature of the semiconductor laser element is kept almost constant, or when the heat sink temperature is kept almost constant by a thermoelectric cooling element. It can be used to

As an example, the output stability when there is a temperature change of ±3°C around a room temperature of 25°G was ±20;b.

When the laser beam is modulated, the provision of a low-pass filter in the amplifier 6 is the same as in the embodiment shown in FIG.

Further, it is desirable to provide a current limiting device in the power supply 14 in order to prevent the current value flowing through the laser element from becoming too large and entering an unstable region where the laser output decreases as the current increases.

In addition, in the case of the embodiment shown in FIG. 3, the cavity of the semiconductor laser is composed of two opposing reflecting surfaces, but the reflection breakage can be caused by cleaving, polishing, etching, ion milling, etc. In addition to those that utilize a flat surface obtained using a method, the present invention can also be applied to those that utilize Bragg reflection obtained by a periodic structure provided in the active layer of a laser or in the propagation path of laser light. can.

This is because even in the latter case, it can be considered that there are equivalently two reflecting surfaces.

As explained above, according to the present invention, the optical output for information processing of an information processing device becomes constant, making it possible to operate the device stably and perform highly reliable information processing, and at the same time, it is possible to operate the device stably and perform highly reliable information processing. Since the light source is used, the light source can be made smaller, and information processing devices can be made more compact.

[Brief explanation of the drawing]

FIG. 1 is a comparable block diagram of an embodiment of the semiconductor laser device according to the present invention, and FIG. 2 shows the relationship between the laser output, current, and heat sink temperature of a semiconductor laser that operates continuously or at a near-continuous duty ratio. The characteristic diagram and FIG. 3 are a cross-sectional view of a second embodiment of a semiconductor laser device according to the present invention and a block diagram of a control circuit. In FIGS. 1 to 3, 1: semiconductor laser element, 2
: Active layer of semiconductor laser, 3, 4: Laser light, 5: Photodetector, 6: Amplifier, 7: Power supply for control circuit and thermoelectric cooling element, 8: Heat sink, 9: Insulating layer, 10: Metal plate, 1
1: Insulating layer, 12: Thermoelectric cooling element, 13: Radiation fin,
14: Power supply for semiconductor laser, 14: Control circuit and power supply for semiconductor laser.

Claims (1)

[Scope of Claims] 1. Laser light emitted from a semiconductor laser element used as light for information processing in a semiconductor laser device that emits the above-mentioned laser light of an information processing device that processes predetermined information using semiconductor laser light. a light-receiving element that receives laser light emitted from the opposite side; a detection means that detects a variation in the light output received by the light-receiving element; and a detection means that controls the light output of the semiconductor laser element based on the variation. 1. A semiconductor laser device comprising: a control means, wherein the output of the information processing light is controlled by the control means. 2. A semiconductor laser device according to claim 1, wherein the control means is means for controlling human power supplied to the semiconductor laser element. 3. The semiconductor laser device according to claim 1, wherein the control means is means for controlling an input to a thermoelectric cooling element that controls the temperature of the semiconductor laser element. 4. Information processing device that processes predetermined information using semiconductor laser light In the semiconductor laser device that emits the above-mentioned laser light, the laser light emitted from the opposite side to the laser light emitted from the semiconductor laser element used as light for information processing is a light-receiving element that receives the laser beam; a detection means that compares the output of the light received by the light-receiving element with a preset reference value and detects a variation in the received light output; A semiconductor comprising: a control means for controlling the light output of the semiconductor laser element so as to cancel out fluctuations in the light reception output of the light receiving element, and the light output of the information processing is controlled by the control means. laser equipment. 5. A semiconductor laser device according to claim 4, wherein the control means is means for controlling input supplied to the semiconductor laser element. 6. The semiconductor laser device according to claim 4, wherein the control means is means for controlling an input to a thermoelectric cooling element that controls the temperature of the semiconductor laser element.